The present invention relates to a nozzle head for use in an ink jet printer. A nozzle head having the features specified hereinbelow is disclosed in EP-A-0 402 172. This nozzle head comprises a channel plate defining a linear array of equidistant nozzles and a plurality of parallel ink channels, each connected to a respective one of the nozzles. On one side of the channel plate there is disposed an array of elongate fingers projecting towards the nozzle plate and extending in parallel with the ink channels. The ends of these fingers facing away from the channel plate are interconnected by a plate-like backing member which is formed integrally with the fingers. The fingers and the backing plate are made of a piezoelectric ceramic material. Every second finger is provided with electrodes and serves as an actuator which, when a print signal is applied to the electrodes, compresses the ink liquid contained in the associated ink channel, so that an ink droplet is expelled from the nozzle. The other fingers intervening between the actuators serve as support members which are rigidly connected to the channel plate so that they can absorb the reaction forces generated by the actuators.
Since a support member is provided between each pair of consecutive actuators, each actuator is substantially shielded against the reaction forces from its neighbors, so that undesired cross-talk between the various channels is reduced.
In this conventional nozzle head, the pitch of the support members, i.e. the distances at which the support members are disposed in the direction of the linear nozzle array, is equal to the pitch of the nozzles. As a consequence, the total number of fingers per unit length in the direction of the linear nozzle array, i.e. the density with which the fingers have to be arranged, is twice the density of the nozzles. Since intricate manufacturing problems are involved in preparing a high-density array of fingers, it becomes difficult to reduce the pitch of the nozzles in order to improve the resolution of the printer.
It is accordingly an object of the present invention to provide a nozzle head for high-resolution printing which can easily be manufactured and nevertheless suppress cross-talk between the individual channels.
According to the present invention, the pitch of the support members is larger than that of the nozzles, so that there is no longer a one-to-one relationship between the support members on the one hand and the actuators, the ink channels and the nozzles on the other hand. The mean density of the fingers will accordingly be smaller than twice the density of the nozzles. Of course, the support members have to be arranged such that they are connected to the dam portions of the channel plate separating the individual ink channels, whereas the actuators have to be disposed adjacent to the ink channels and must not overlap with the dam portions. However, since the support members may be slightly offset from the centers of the dam portions and/or the actuators may be slightly offset from the centers of the ink channels, it is possible to distribute the fingers in such a manner that their spacings are comparatively large, so that even for a nozzle array with a reduced pitch, the array of fingers can be manufactured with conventional techniques, e.g. by cutting grooves into a block of piezoelectric material.
In a preferred embodiment, the ratio between the densities of the fingers and nozzles is 3:2, and every third finger is a support member. This embodiment has the advantage that each actuator has as its neighbors a support member on the one side and another actuator on the other side, so that for any pair of ink channels, the configurations of actuators and support members in the vicinity of these ink channels are either identical or mirror-symmetric. As a result, the configurations of actuators and support members will not lead to any differences in the generation of droplets.
The fingers may be arranged equidistantly, which has the advantage that the manufacturing process can be very simple and efficient.